16 INTRODUCTION. 



vesicle which attains the thirtieth of a millemetre in len2:th. 

 It is entirely invested with cilia, rather short, the vibration 

 of which determines the advancing movement of the spore. 

 M. Unger first pointed out these organs in a great and cu- 

 rious work recently published.* The interest of the subject, 

 and the facility of procuring each day fresh specimens, from 

 January until May, determined me to study that plant with 

 care. I proceed to give the result of my observations. 



The tufts of the Vaucheria ( V. clavatd) are formed of a 

 network of filaments, cylindrical, branched, continuous, which 

 enclose the green granules (endochrome) and colourless mu- 

 cilage. At the period of the formation of the spore, the 

 extremity of its filaments swell up in the form of a club, and 

 the green matter becomes there condensed, so as to assume a 

 blackish tint. (See Plate II. Jig. 21, 22.) Near the base of 

 the enlargement the granules are seen separated the one from 

 the other, leaving an empty space as if the mucilage had 

 condensed itself in its turn, and driven the granules above 

 and below. This displacement continues until the endo- 

 chrome forms well-defined lines on each side. (See Plate II. 

 Jig. 23.) Then the great change takes place, which consists 

 in the operation which we are about to describe, viz. the 

 separation of the mother plant and of the reproductive body, 

 subsequently clothed with a membrane proper to itself 

 (epispore), possessing a distinct organization. 



Although this phenomenon continues but for a few 

 minutes, it is easy to observe it, since the movement of the 

 granules is almost insensible. Moreover, the separation is 

 not discontinued after the first time. I have seen the 

 operation thrice repeated upon the same filament. 



The spore then takes the form o^ Jig. 24., that of an elon- 

 gated oval vesicle, whose two divisions are nearly black by 

 the condensation of the endochrome, the inferior division 

 containing much less endochrome. It is then that the crisis 

 approaches : the superior extremity suddenly becomes pro- 

 truded, the granular fluid empties itself into the protruded 



* Die Pflanzc in Momente der ThicrwerduniT. Wieii. 1843. 



